In traditional wireless telecommunications systems, transmission equipment in a base station transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an enhanced node B (ENB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment. Devices that might be used by users in a telecommunications network can include both mobile terminals, such as mobile telephones, personal digital assistants, handheld computers, portable computers, laptop computers, tablet computers and similar devices, and fixed terminals, such as residential gateways, televisions, set-top boxes, and the like. Such mobile and fixed devices will be referred to herein as user equipment or UE.
A group of LTE-based cells might be under the control of a single entity known as a central control. The central control typically manages and coordinates certain activities with a group of cells such as scheduling the transmission of broadcast/multicast services from the ENBs under its control to the UEs being served by the ENBs.
Services that might be provided by LTE-based equipment can include broadcasts or multicasts of television programs, streaming video, streaming audio, and other multimedia content. Such services are commonly referred to as multimedia broadcast multicast services (MBMS). An MBMS might be transmitted throughout a single cell or throughout several contiguous or overlapping cells. A set of cells receiving an MBMS can be referred to as a service area. A service area and a region under the control of a central control do not necessarily coincide. For example, a central control might specify that a first subset of cells under its control will deliver a first MBMS and that a second subset of cells under its control will deliver a second MBMS.
The transmission of an MBMS can include two components, a multicast control channel (MCCH) and a multicast traffic channel (MTCH). The MTCH delivers the actual content of the MBMS while the MCCH delivers control information related to the MBMS. The MCCH might include key control information that specifies how the content in the MTCH is to be delivered.
An MBMS may be communicated from an ENB to a UE using point-to-point (PTP) communication or point-to-multipoint (PTM) communication. PTP communication is similar to conventional cellular network communication in that there is a dedicated radio bearer between the ENB and a UE. PTP communication from the ENB may enable high quality communication with the UE. However, when an ENB communicates with a large number of UEs using PTP communication, a substantial amount of overhead may be required for establishing and maintaining the PTP communications and a substantial amount of the available spectrum may be occupied.
PTM communication may include utilizing a dedicated channel or dedicated carrier to broadcast data or services to multiple UEs. While a certain amount of overhead may be required to initiate a broadcast PTM communication, the overhead is relatively small and may not vary in relation to the number of UEs. That is, as more UEs utilize the broadcast data or services, the overhead required to establish and maintain the broadcast PTM communication remains approximately the same. Broadcast PTM communications may also improve spectral efficiency as the number of UEs increases because no new transmissions are required for newly added users. In some cases, the quality of broadcast PTM communications may be less than that for PTP communications since there is little or no communication from the UEs to the ENB, and because of power considerations and other factors that may reduce the relative quality of the communication.
When multiple cells overlap, a UE within the overlapped region can receive transmissions from multiple ENBs. It is well known in the art that when a UE receives substantially identical data from a plurality of ENBs, the transmissions from the ENBs can augment one another to provide a signal of significantly higher quality than would be the case if only one ENB were transmitting the signal. That is, a higher signal-to-noise ratio can be achieved when substantially the same data is transmitted at substantially the same time on substantially the same resource with substantially the same modulation and coding. Conversely, destructive interference can occur when different data signals are present in the same region at the same time.
A region in which a plurality of substantially identical signals are present is known as a single frequency network, or SFN. In the case where all of the ENBs in a service area are transmitting an MBMS with substantially identical signals, the service area would be an SFN and augmentation of the signals would occur. However, if the ENBs were transmitting the MBMS with different signals, for example, on a different resource, the service area would not be an SFN and the signals might destructively interfere with one another.